The mechanisms of hypoxemia and of declining gas exchange in patients with treated and untreated pneumonia due to pneumocystis is not clean. A microtechnique for the measurement of surfactant lipids from Bronchoalveolar Lavage Fluid has been developed. In a preliminary study, 29 samples were studied. There is evidence of surfactant lipid breakdown with an increase in lysophosphatidyl choline. There is also evidence of increased Phospholipase A2 activity in the lavage fluid of these patients. This paper was published in 1992. The importance of these studies is that these observations may allow for the development of new or different therapies in this patient population. This study has been extended to evaluate the effect of corticosteroid administration on surfactant lipid levels in the BAL of HIV infected patients with Pneumocystis pneumonia. In a longitudinal study of BAL surfactant in patients with pneumocystis carinii pneumonia, BAL surfactant dipalmitoyl phosphatidyl choline (DPPC) was measured at Day 0 and Day 10 using a capillary column gas chromatograph. The BAL DPPC levels of patients receiving adjunctive corticosteroid therapy were compared to those not receiving this therapy. The BAL surfactant PC levels were depressed (about 25% of normal) at Day 0 in both groups and returned toward normal by Day 10. There was no difference between the groups at Day O and Day 10 current studies are focusing on changes in BAL surfactant DPPC at day 3-5 after initiation of therapy. This study demonstrates a reduction in pulmonary surfactant lipid in patients with pneumonia It raises the possibility of new approaches to the therapy of respiratory failure due to pneumocystis carinii.